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Electromagnetic induction

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Electromagnetic induction is where a voltage or current is produced in a conductor by a changing magnetic flux. It may happen when a magnet is moved in a solenoid, thus changing the magnetic flux.

Magnetic flux

When a coiled wire is introduced near a magnet, the magnetic lines of force pass through the coil. This causes the magnetic flux to change. Magnetic flux is represented by the symbol [math]{\Phi}[/math], therefore we can say that [math]{\Phi}[/math] = BAcos(a) and the resulting unit will be [math]Tm^2[/math], where T is the unit for magnetic field and [math]m^2[/math] is the unit for area.

The changing magnetic flux generates an electromotive force (EMF). This force moves free electrons in a certain way, which constitute a current.

Faraday's law

Michael Faraday found that an electromotive force is generated when there is a change in magnetic flux in a conductor.

His laws state that:

[math] \mathcal{E} = {-{d\Phi} \over dt}[/math]


[math]\mathcal{E}[/math] is the electromotive force, measured in volts;

[math]{d\Phi}[/math] is the change in magnetic flux, measured in webers;

[math]dt[/math] is the change in time, measured in seconds.

In the case of a solenoid:

[math] \mathcal{E} = {-N{d\Phi} \over dt}[/math]


N is the number of loops in the solenoid.

Lenz's law

The negative sign in both equation above is a result of Lenz's law, named after Heinrich Lenz. His law states that the electromotive force (EMF) produces a current that opposes the motion of the changing magnetic flux.

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